Mesh Networking with OLSR

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Contents

General

What is mesh networking?

Mesh networking is used to route data, voice and instructions between nodes (typically routers). A mesh network typically consists of 2 or (many) more nodes, which exchange information about their connection-status with each other (routing updates), so that every node knows, which path he has to take to reach any other node in the mesh. When a node wants to reach another node that is not directly connected, the traffic flows over other nodes, until the final node is reached (hopping) -each node that the traffic flows through is called a hop.

Why mesh networking?

Mesh networks differ from other networks in that the component parts can all connect to each other via multiple hops. Mesh networks are self-healing: the network can still operate even when a node goes down or a connection drops. The result is a very reliable network.

Benefits of mesh networking

  • self organizing
  • self-healing
  • low system maintenance needed
  • robust due dynamic route recalculation

Disadvantages of mesh networking

  • additional network traffic

The exchange of routing information (routing updates) can produce a lot of traffic-overhead, also every device that takes part of a mesh must have enough cpu/ memory to have an overview of all other routers and how to reach them. (routing table). A full routing table can get very large - as seen in BGP-Routing: a full BGP table needs 2GB of memory (300.000 active routes). There is also a danger of routing-loops that can appear because of weak routing information.

OLSR

General

OLSR is a dynamic linkstate Protocol which collects link data and dynamically calculates the best routes within the network.

Links:

http://en.wikipedia.org/wiki/OLSR
http://www.olsr.org

Parameters

General:

  • IpVersion
  • AllowNoInt
  • Pollrate
  • TcRedundancy
  • MprCoverage
  • LinkQualityFishEye
  • LinkQualityWinSize
  • LinkQualityDijkstraLimit

per Interface:

  • HelloInterval
  • HelloValidityTime
  • TcInterval
  • TcValidityTime
  • MidInterval
  • MidValidityTime
  • HnaInterval
  • HnaValidityTime
  • LinkQualityMult

HNA4

IcpConnect

Plugins:

Sample config file:

DebugLevel              0
IpVersion               4
AllowNoInt              yes
Pollrate                0.1
TcRedundancy            2
MprCoverage             7
LinkQualityFishEye      1
LinkQualityWinSize      100
LinkQualityDijkstraLimit 0 7.0
LoadPlugin "olsrd_txtinfo.so.0.1"
{
       PlParam "Accept" "127.0.0.1"
}
Hna4
{
}
IpcConnect
{
       MaxConnections  1
       Host            127.0.0.1
       Net 192.168.1.0 255.255.255.0
}
LinkQualityLevel 2
UseHysteresis no
Interface "eth1"
{
       HelloInterval           5.0
       HelloValidityTime       90.0
       TcInterval              3.0
       TcValidityTime          270.0
       MidInterval             15.0
       MidValidityTime         270.0
       HnaInterval             15.0
       HnaValidityTime         90.0
       LinkQualityMult 10.100.2.5 0.5
}
Interface "vlan1"
{
       HelloInterval           5.0
       HelloValidityTime       90.0
       TcInterval              3.0
       TcValidityTime          270.0
       MidInterval             15.0
       MidValidityTime         270.0
       HnaInterval             15.0
       HnaValidityTime         90.0
       LinkQualityMult 10.100.2.5 0.5
}

Setup

DD-WRT > v.23 SP3

Try the following steps to get OLSR running: Under Wireless -> Basic Settings

  • enable your prefered networking mode (use adhoc mode)
  • set your wlan mode (b,g,mixed...)
  • set your SSID
  • set your channel
  • unbridge the wlan
  • set an ip
  • set the network mask to e.g.255.255.255.0

Under Setup -> Advanced Routing

  • set Operating Mode to OLSR
  • keep the basic olsr settings. they are ok for the first tests
  • add the correct wlan interface to olsr (e.g. on most buffalos its eth1, WRT350N its eth0, MR3201A its ath0)
  • keep the interface settings for testing

Enabling NAT routing

In Gateway mode the router performs NAT, while in other modes it doesn't. When you switch the Advanced Routing Operating Mode to OLSR Router, it turns off NAT. Here is how to turn the NAT back on, assuming you followed the instructions on unbridging the wlan.

Under Administration -> Commands paste the script below into Commands and click "Save Firewall" Do this on each device.

iptables -t nat -A POSTROUTING -o $(nvram get wan_ifname) -j MASQUERADE
iptables -t nat -A POSTROUTING -o $(nvram get wl0_ifname) -s $(nvram get eth1_ipaddr)/$(nvram get eth1_netmask) -d $(nvram get eth1_ipaddr)/$(nvram get eth1_netmask) -j MASQUERADE
iptables -t nat -A POSTROUTING -o $(nvram get lan_ifname) -s $(nvram get lan_ipaddr)/$(nvram get lan_netmask) -d $(nvram get lan_ipaddr)/$(nvram get lan_netmask) -j MASQUERADE

External Links



--Sash 22:00, 7 June 2008 (CEST)

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